The invention relates to a method for joining components.
Modern gas turbines, particularly aircraft engines, must meet extremely high demands with regard to reliability, weight, power, economy and service life. In the last few decades, aircraft engines that fully meet the requirements listed above and have achieved a high level of technical perfection have been developed, especially in the civilian sector. The choice of materials, the search for suitable new materials and novel production methods, among other things, plays a decisive role in the development of aircraft engines. The most important materials used nowadays for aircraft engines or other gas turbines are titanium alloys, nickel alloys and high strength steels. High strength steels are used for shaft parts, gear parts, the compressor housing and the turbine housing. Titanium alloys are typical materials for compressor parts. Nickel alloys are suitable for the hot parts of the aircraft engine. Precision casting and forging are the primary production methods known from the prior art as production methods for gas turbine components made of titanium alloys, nickel alloy or other alloys. All highly stressed gas turbine components such as, for example, the blades for a compressor, are forged parts. However, rotor blades and guide blades of the turbine are usually designed as precision cast parts.
When producing, for example, integrally bladed gas turbine rotors, it is necessary to join components with one another that differ in terms of their material structure as well as their hardness. Joining these types of parts is normally accomplished in practice using inductive high-frequency pressure welding, wherein, in the case of inductive high-frequency pressure welding, components to be joined with one other are inductively heated in the region of the joining surfaces of the components in order to melt the material structure, and wherein after the melting, the components to be joined with one another are pressed together or compressed by applying a compressive force. Particularly when, for example, a cast component is supposed to be joined to a forged component, wherein the cast component has a greater hardness than the forged component, completely removing the melted material from the joining region when pressing the components together presents difficulties in the case of inductive high-frequency pressure welding.
This can result in the formation of grain boundary incipient melting, which has a negative impact on the so-called HCF strength of the joint, because such grain boundary incipient melting can be the starting point for microscopic cracks. As a result, there is a need for a method for joining these types of components by means of inductive high-frequency pressure welding, in which there is no danger of grain boundary incipient melting occurring in the region of the joint.
Reference is made by way of example to German Patent Document No. DE 198 58 702 A1 as the prior art, which discloses inductive high-frequency pressure welding as a joining method for gas turbine components.
Starting from here, the present invention is based on the objective of proposing a novel method for joining components.
According to the invention, the joining surface of the first component having the first hardness, which is greater than the second hardness of the second component, is pre-contoured in a spherical, conical or convex manner prior to joining the two components.
In terms of the invention, the harder component of the components to be joined to one another is pre-contoured in the region of its joining surface in a spherical, conical or convex manner so that, with the application of the compressive force during inductive high-frequency pressure welding, a complete displacement of the melted material from the joining region of the components being joined with one another is possible. As a result, all liquid phase components can be reliably removed from the joining region so that no grain boundary incipient melting is able to occur in the joining region. The joining region between the components is therefore the same as a forged structure, which has good HCF strength.
Preferred further developments of the invention are yielded from the subsequent description. Without being restricted hereto, exemplary embodiments of the invention are explained in greater detail on the basis of the drawing.